1. Field of the Invention
The present invention relates to a method of preventing dust from adhering to a wall, such as the side wall of an incinerator or the walls of a furnace, and to an incinerator and a melting furnace which are provided with means for preventing dust from adhering to interior surfaces thereof.
2. Description of the Prior Art
A prior art water injection nozzle for cooling hot exhaust gas containing a large quantity of dust is shown in FIG. 8.
The water injection nozzle 1 extends into a gas cooling chamber 2 through a refractory wall 3. Water 4 for cooling the gas is introduced from a water inlet 5 of the water injection nozzle 1 into a pipe 5a extending axially in the nozzle 1. The water 4 is thus injected from the tip of the nozzle 1 into the gas cooling chamber 2. Excess water flows to a water return line via a water outlet 6 of a pipe 6a which surrounds the pipe 5a. A sleeve 10, on the other hand, surrounds the nozzle 1. Nozzle cooling and purging air or inert gas 9 is introduced into the gas cooling chamber 2 from the tip of the nozzle 1 through the space which is defined between the sleeve 10 and the nozzle 1.
Also, in recent years, the ash from a furnace is melted to thereby reduce the volume of the ash and render it harmless. FIG. 9 shows one example of a prior art furnace in which such a melting of the ash is carried out by plasma.
In FIG. 9 reference numeral 114 designates a furnace wall; numeral 115 designates a slag outlet; numeral 116 designates an exhaust gas duct; numeral 117 designates an electrode; numeral 118 designates an electrode support device; numeral 119 designates a power supply; numeral 120 designates molten slag; numeral 121 designates inert gas; numeral 122 designates an ash feeding conveyor; numeral 123 designates an ash hopper; numeral 124 designates a batch type feeder; numeral 125 designates an ash inlet port; numeral 126 designates a dust collector; numeral 127 designates an induced draft fan; numeral 128 designates a water bath for quickly cooling molten slag; numeral 129 designates a slag hopper; and numeral 130 designates a cooling water circulation pump.
In this furnace, substances having low-boiling temperatures in the ash may volatilize, and when the vapors of volatilization cool at the exhaust gas duct 116, the vapors condense on the duct 116 or dust discharged from the furnace may adhere to or become deposited on the duct 116. Thus, the duct 116 becomes clogged. Moreover, slag may cool down and likewise clog the slag outlet 115. These problems create a bottleneck in a furnace of this kind because they form an obstruction to the continuous operation thereof.
In the water injection nozzle of the prior art, as shown in FIG. 8, the water 4 is injected from the tip of the water injection nozzle 1 at a high speed and thus generates a wake (or vortexes) 24 as indicated by arrow b. Dust 22, which is being carried by hot exhaust gas 16 flowing in the direction of arrow a, is caught in the wake 24, thus producing flower 23 around the nozzle or otherwise causing the dust to adhere to the furnace wall.
As the amount of flower 23 increases, it begins to directly impede the injected water. Finally, a stable injection of water is prevented, and the flower 23 is wetted together with the refractory wall 3 by such an unstable water injection, whereby the refractory wall 3 is deteriorated. Moreover, when the exhaust gas 16 contains hydrogen chloride (HCl) and/or sulfur oxide (SOx) and is absorbed by the wet flower 23, acidic water formed by the HCl and/or SOx seeps into the refractory wall 3 and has the potential to corrode a shell 12 forming the outer casing of the furnace.